Effective use of transgenes for the treatment of inherited and acquired disorders requires efficient delivery of transgenes. Various vector systems have been developed that are capable of delivering a transgene to a target cell. However, there remains a need to improve efficiency of available gene transfer methods. Improved efficiency is desirable both to increase the ability of the vector to correct the cellular defect, and to decrease the required amount of the vector and thereby reduce toxicity.
Transfer of the cystic fibrosis transmembrane conductance regulator (CFTR) cDNA to airway epithelia of patients with cystic fibrosis (CF) provides an example of the successful use of gene transfer to correct a cellular defect, i.e., the CF defect in electrolyte transport. Vector systems including adenoviral vectors (Zabner et al. (1993) Cell 75: 207; Knowles et al. (1995) New Engl. J. Med. 333: 823; Hay et al. (1995) Hum. Gene. Ther. 6: 1487; and Zabner et al. (1996) J. Clin. Invest. 97: 1504) and cationic lipids (Caplen et al. (1995) Nat. Med. 1: 39) are capable of transferring the CFTR cDNA and expressing CFTR in mature ciliated human airway epithelia. The successful delivery of CFTR in such cells is manifest in a functional chloride ion channel in the treated cells
Currently used adenoviral vectors are less than optimal in delivering the CFTR cDNA to airway epithelia because the binding of the virus to the apical surface of the epithelium is limited. Grubb et al. (1994) Nature 371: 802. The limited infection can be partially overcome by increasing the contact time between the virus and the apical surface. Zabner et al. (1996) J. Virol. 70: 6994.
Cationic lipid vector-mediated gene transfer to mature human airway epithelia is also suboptimal. Caplen et al. (1995) Nat. Med. 1: 39. While it appears that cationic molecules bind to the cell surface and in some cases are taken up by the cell, important barriers to transgene expression may be release of DNA from the endosome, entry into the nucleus, release of DNA from the cationic molecule, and transcription of the DNA. Zabner et al. (1995) J. Biol. Chem. 270: 18997.
Gene transfer systems that combine viral and nonviral components have been reported. Cristiano et al. (1993) Proc. Natl. Acad. Sci. USA 90: 11548; Wu et al. (1994) J. Biol. Chem. 269: 11542; Wagner et al. (1992) Proc. Natl. Acad. Sci. USA 89: 6099; Yoshimura et al. (1993) J. Biol. Chem. 268: 2300; Curiel et al. (1991) Proc. Natl. Acad. Sci USA 88: 8850; Kupfer et al. (1994) Hum. Gene Ther. 5: 1437; and Gottschalk et al. (1994) Gene Ther. 1: 185. In most cases, adenovirus has been incorporated into the gene delivery systems to take advantage of its endosomolytic properties. The reported combinations of viral and nonviral components generally involve either covalent attachment of the adenovirus to a gene delivery complex or co-internalization of unbound adenovirus with cationic lipid: DNA complexes. Further, the transferred gene is contained in plasmid DNA that is exogenous to the adenovirus. In these formulations, large amounts of adenovirus are required, and the increases in gene transfer are often modest.
Accordingly, there is a need in the art for improved vector systems for the efficient delivery of transgenes to target cells. The present invention overcomes the limitations associated with adenoviral vectors and cationic lipid vectors while retaining the desirable features of each vector system.